Role of sp2 C cluster size on the field emission properties of sulfur-incorporated nanocomposite carbon thin films

The electron field emission properties of sulfur-incorporated nanocomposite carbon thin films grown by hot-filament chemical vapor deposition were investigated as a function of film microstructure. The in-plane correlation length (L-a) of the sp(2) C clusters in these films was determined from the intensity ratio of the D and G bands [I(D)/I(G)] in the visible Raman spectra using a phenomenological model. The turn-on field was found to decrease with increasing sp(2) C cluster size in the range of 0.8-1.4 nm. The lowest turn-on field found was 4.0 V/mum corresponding to films having sp(2) C clusters of around 1.4 nm and conductivity of 30 Ohm(-1) cm(-1). These findings are discussed in terms of a reduced field emission barrier brought about by the incorporation of sulfur and the need for relatively longer conductive paths capable of withstanding the relatively large emission currents. (C) 2002 American Institute of Physics.